Photonic approach for Doppler-frequency-shift and angle-of-arrival measurement with direction unambiguity and high precision

A novel, to the best of our knowledge, scheme based on a dual-drive Mach-Zehnder modulator (DDMZM) is proposed for Doppler-frequency-shift (DFS) and angle-of-arrival (AOA) measurement without direction ambiguity. The echo signal from one antenna is coupled with a local oscillator and then fed into the upper RF port of the DDMZM, and the echo signal from the other one is directly fed to its lower RF port. The generated two first-order optical sidebands are separated by an interleaver to form two channels and then detected by two identical low-speed photodiodes, and so both magnitude and orientation of the AOA and DFS can be deduced from the power and frequency of the beating signals. The AOA measurement without direction ambiguity can be achieved by comparing the power of beating signals from two channels. In addition, through operating the DDMZM at different transmission points for different AOA measurement ranges, the range of high-precision AOA measurement can be extended. The system has the low complexity and high stability because only a DDMZM is used. The simulation results demonstrate the measurement of the DFS in the range of 500 kHz with errors <0.05Hz and the AOA from -90∘ to +90∘ with error <0.8∘.